Criticism of a £9 million taxpayer-funded pro-EU leaflet continued even as it was due to begin landing on doormats.
Eurosceptic Tory backbenchers are threatening to seek to derail George Osborne's Budget in protest at what they say is an unfair skewing of the referendum debate.
Ex-cabinet minister Liam Fox wrote to Prime Minister David Cameron calling for the case for a "leave" vote on June 23 to be included in the publication.
But it has already been printed and is expected to arrive in some households in England from today - with delivery to Scotland, Wales and Northern Ireland delayed until after elections to devolved governments in May.
More than 200,000 people have signed a petition demanding that the Government abandons the plan and Europe Minister David Lidington will be forced to defend the controversial move when he makes a statement in Parliament.
Veteran Tory Eurosceptic Sir Bill Cash said he will table an amendment to the Finance Bill, which enacts the Budget, which could block its progress if passed in a Commons vote.
Sir Bill, chairman of the Commons European Scrutiny Committee, said: "I am putting down a very big indicator of the anger and, I would go so far as to say, the fury of people who are being asked to pay - and there are millions of them in the country - for a pamphlet to 27 million homes."
Sir Bill accused ministers of "breaking the principle of fairness" over the conduct of the referendum.
As ministers prepared for a fresh round of conflict within the Tory party, Mr Cameron warned the UK's security was at risk if the country voted to leave the EU and accused Brexit campaigners of "gambling with our country's fortunes".
Writing in the i newspaper, Mr Cameron said: "The world is increasingly divided, so it's vital we choose unity. Western values are under threat - we must stand with those who share them."
He says the the leaflet is "money well spent" and insists it is "necessary and right" to put the Government's case for staying in but critics - including Justice Secretary Michael Gove - say it is unfair and a waste of public money.
In his letter, Dr Fox told the PM: "I agree with you that the public wants facts - but the proposed leaflet is a collection of opinions, assertions and suppositions.
"The current proposal effectively doubles the budget for the Remain campaign and will offend the natural spirit of fair play that is so much a part of the character of the British people.
"If the Government intends to go ahead with this publication, then I suggest you consider correcting the imbalance by allowing the opposite side to include the alternative view."